Center for By-Products Utilization

Transcription

1 Center for By-Products Utilization CONCRETE CONTAINING PULP AND PAPER MILL RESIDUALS By Tarun R. Naik, Yoon-moon Chun, and Rudolph N. Kraus Report No. CBU REP-470 June 2002 For Presentation at the Technical Session on Recycling Concrete and Other Materials for Sustainable Development at 2003 ACI Spring Convention, Vancouver, British Columbia, Canada, April 1, Department of Civil Engineering and Mechanics College of Engineering and Applied Science THE UNIVERSITY OF WISCONSIN-MILWAUKEE

2 CONCRETE CONTAINING PULP AND PAPER MILL RESIDUALS By Tarun R. Naik 1, Yoon-moon Chun 2, and Rudolph N. Kraus 3 ABSTRACT: Fibrous residuals generated from pulp and paper mills were included in concrete. In general, at somewhat lower compressive strength, concrete containing the residuals showed higher average residual-strength, equivalent length change (drying shrinkage), and equivalent or lower chloride-ion penetration resistance and abrasion resistance when compared with reference concrete made without residuals. On the other hand, the residuals concrete showed generally much higher freezing-and-thawing resistance and salt-scaling resistance than the reference concrete. Key words: concrete; durability; freezing-and-thawing resistance; microfiber reinforcement; pulp and paper mill residual solids; recycling; salt-scaling resistance. 1 Director, UWM Center for By-Products Utilization, University of Wisconsin-Milwaukee, P.O. Box 784, Milwaukee, WI 53201, Ph: (414) , Fax: (414) , tarun@uwm.edu 2 Research Assistant, UWM Center for By-Products Utilization 3 Assistant Director, UWM Center for By-Products Utilization - 1 -

3 INTRODUCTION Pulp and paper mill wastewater treatment plant residuals (also called sludge) are the solid residue removed from mill wastewater before the water is discharged into the environment or reused in the mill. Residuals are removed via a two-step process of treating the wastewater [1, 2, 3, 4, 5]. Primary residual is the solids removed from the primary clarifier. Primary clarification is usually carried out by sedimentation, but in some cases by dissolved air flotation. In the sedimentation process, chemical additives are used to make non-settleable solids settleable through flocculation. Primary residual consists mainly of cellulose fibers and papermaking fillers (kaolinitic clay, calcium carbonate, and/or titanium dioxide). In some cases, ash generated at mill and inert solids rejected during chemical recovery processes become part of the primary residual. The water clarified by the primary treatment is passed on to the secondary treatment. Secondary treatment is usually a biological process in which micro-organisms convert soluble organic matter to carbon dioxide and water while consuming oxygen. Secondary residual is mainly microbial biomass (also called biosolids) grown during this process and removed through clarification. Many times primary and secondary residuals are combined to facilitate handling. In most cases, the residual solids are dewatered before disposal or beneficial use. In 1995, U.S. pulp and paper industry generated about 5.3 million metric dry tons of mill wastewater treatment residuals, which is approximate equivalent to 15 million metric tons of wet residuals. About half of this was disposed in landfills/lagoons, a quarter was burned, one-eighth was applied on farmland/forest, one-sixteenth was reused in mills, and the rest one-sixteenth was used in some other ways [6]

4 Due to increasing cost of landfilling, increasingly stringent environmental regulations, and potential long-term environmental liabilities, the percentage of the residuals disposed in landfills has decreased considerably over the years [2, 3, 6]. However, still significant amount of residuals needs to be diverted from landfilling. Numerous projects have been conducted on the use of cellulose fibers as reinforcement in pressed cement sheets and mortar. Cellulose fiber reinforced cement-based sheet composites showed considerably higher flexural toughness than plain cement-based sheets [7, 8, 9, 10, 11]. Use of cellulose fibers reduced the extent of shrinkage cracking of mortar [12] and improved the resistance of cement-based composites to freezing and thawing [11]. A group of researchers conducted a series of investigations on mechanical properties and durability of steel or carbon microfiber reinforced cement pastes and mortars [13, 14, 15]. Properties of the steel and the carbon micro-fibers used in these investigations are presented in Table 1. Properties of virgin wood cellulose fibers [1, 16] are also presented for comparison. Table 1. Properties of Microfibers [1, 13, 14, 15, 16] Properties Type of Microfibers Steel Carbon Virgin Wood Cellulose Length, L (mm) Diameter, D (µm) 12.6* (14-26) Aspect Ratio, L/D ( ) Specific Gravity Tensile Strength (MPa) Modulus of Elasticity (GPa) * Equivalent diameter. Actual cross-section = 5 µm x 25 µm. Using equivalent diameter when cellulose fibers are collapsed (flat)

5 It is noteworthy that the steel and carbon micro-fibers are comparable to cellulose fibers in many aspects. The steel micro-fibers were comparable to virgin cellulose fibers in length, diameter, aspect ratio (length/diameter), and tensile strength, but had higher specific gravity (7.85 vs. 1.50) and modulus of elasticity (200 GPa vs GPa) than cellulose fibers. The carbon micro-fibers were similar to cellulose fibers in diameter, specific gravity, tensile strength, and modulus of elasticity, but were longer (10 mm vs. 2-4 mm) and slender (L/D: 556 vs ) than cellulose fibers. Steel micro-fibers and carbon micro-fibers had no significant influence on compressive strength, drying shrinkage, and chloride-ion penetration resistance of mortars [13]. However, use of the micro-fibers significantly improved freezing-and-thawing (F&T) resistance and deicer-salt scaling resistance of pastes [14] and mortars [13, 14]. The improvement of F&T and salt-scaling resistance was attributed to the ability of micro-fibers to reduce the rate of crack propagation. Addition of steel micro-fibers resulted in significant improvement of flexural toughness of cement pastes and moderate improvement of flexural toughness of cement mortars [15]. Because of the cellulose fibers present in the residuals, use of the residuals as microfiber reinforcement in concrete could become an economical and beneficial alternative to landfills or other use options. OBJECTIVES The objectives of this research were to establish technical, economical, and performance benefits of using pulp and paper mill residuals in ready-mixed concrete and to establish optimum mixture proportions and production technology for concrete containing residuals

6 Experimental approach included characterization of residuals, development of mixture proportions, and assessment of mechanical properties and durability of concrete containing residuals. RESEARCH SIGNIFICANCE This research was conducted to establish technical, economical, and environmental benefits of using fibrous residuals from pulp and paper mills as microfiber reinforcement in concrete. Currently, most of these residuals are disposed in landfills or burned, incurring increasingly higher disposal cost and potential long-term environmental liabilities to pulp and paper mills. This research demonstrated the potential of the use the residuals as an economical source of cellulose fibers in concrete. Concrete containing the residuals showed generally much higher freezing-and-thawing resistance and deicer-salt scaling resistance than plain concrete. MATERIALS Cement, Fine and Coarse Aggregates, and Chemical Admixtures Type I portland cement used in this research had 340 m 2 /kg fineness by air permeability test, 3.13 specific gravity, and 1.7 % loss on ignition. Oxides composition of the cement was 21.9 % SiO 2, 4.9 % Al 2 O 3, 3.0 % Fe 2 O 3, 64.1 % CaO, 2.4 % MgO, 0 % TiO 2, 0.5 % K 2 O, 0.1 % Na 2 O, and 1.4 % SO 3. The cement met the requirements of ASTM C 150. Fine aggregate (sand) used in this research had 1800 kg/m 3 bulk density, 2.73 specific gravity, 1.3 % absorption, and 2.88 fineness modulus. Crushed stones with a 19-mm maximum size were used as coarse aggregate in this research. The coarse aggregate had 1570 kg/m 3 bulk density, 2.67 specific gravity, and 0.4 % absorption. The sand and the coarse aggregate met the requirements of ASTM C

7 High-range water-reducing admixture (HRWRA) used in this research was a carboxylated polyether liquid admixture meeting the requirements of ASTM C 494 for Type F (HRWRA). Addition rates of this HRWRA recommended by its manufacturer range from 195 to 650 ml/100 kg (3 to 10 fl oz/100 lbs) of cement. Ingredient of HRWRA is shown in Table 2. Table 2. Ingredient of HRWRA Ingredient CAS#* Max. % by mass 2-Propenoic Acid Homopolymer Reaction Product with Polyalkoxyalkylamine * CAS (Chemical Abstracts Service) Registry Number, a unique identifier for a chemical substance. Air-entraining admixture (AEA) in this research was an aqueous solution of neutralized resin acids and rosin acids that complies with ASTM C 260. Addition rates of this AEA recommended by its manufacturer range from 30 to 200 ml/100 kg (1/2 to 3 fl oz/100 lb) of cement for producing air-entrained concrete, containing 4 to 8% entrained air. Ingredients of AEA are presented in Table 3. Table 3. Ingredients of AEA Ingredient CAS# Percent (max.) Resin acids and Rosin acids, maleated, potassium salts Resin acids and Rosin acids, potassium salts Residuals A total of seven sources of pulp and paper mill residuals were used representing a wide variation in the type of wood fibers and processes. Types, physical properties, LOI, and wood fiber content of the residuals are presented in Table 4. Other properties of the residuals are presented in Tables 5 to 7. The concentration of cadmium in paper mill wastewater treatment residuals is well below the most restrictive concentrations specified for land applied municipal sewage - 6 -

8 treatment biosolids [17]. Scanning electron micrographs (SEM) of oven-dry samples of residuals are presented in Fig. 1. Magnification is 100 times. Designation Table 4. Types, Physical Properties, LOI, and Wood Fiber Content of Residuals Type Fiber Origin(s) Moisture Content (%)* Specific Gravity As-Recd Bulk Density (kg/m 3 ) Avg. Fiber Length (mm) Loss On Ignition # (%)* Wood Fiber (%)* C1 Primary Virgin C2 Primary Virgin I Primary Recycled e S Primary Recycled (80 %) + Virgin (20 %) e WG Primary Virgin WV Primary Virgin BR Fiber Reclaim Virgin K e Avg * % of oven-dry (105 C) mass Test was performed using as-received samples. Result is for samples in oven-dry condition. nili i 1 Length weighted average fiber length, LL N n l K # e Using Kajaani FS-100. The rest determined by using Fiber Quality Analyzer. Mass loss upon ignition (at 590 C [ASTM C 1102, Ash in Wood]) Estimated as x LOI at 590 C The rest determined by infrared analysis. N i 1 2 i i Table 5. Mineralogical Composition of Residuals by Powder Diffraction Analysis (% by mass) Mineral Residuals - 7 -

9 C1 C2 I S WG WV Calcite (CaCO 3 ) Kaolinite* (Al 2 Si 2 O 5 (OH) 4 ) Magnesite (MgCO 3 ) 7 Quartz (SiO 2 ) Talc (Mg 3 Si 4 O 10 (OH) 2 ) < 1 3 * Kaolin-type clay Table 6. Oxides* and LOI at 1000 C of Residuals (% by mass) Oxides and Residuals LOI C1 C2 I S WG WV Avg. SiO Al 2 O CaO MgO Fe 2 O TiO K 2 O Na 2 O SO LOI (1000 C) SUM * Determined through X-ray fluorescence (XRF) analysis of ash left after ignition of residuals at 1000 C. Table 7. Main Elements in Residuals by Instrumental Neutron Activation Analysis (in ppm) Element Residuals C1 C2 I S WG WV Avg. (Rank) Aluminum (Al) 56,300 22,900 31,600 21,900 < 1,760 9,320 < 24,000 1 Cadmium (Cd) 1,770 1,860 1,870 1,130 1,700 2,830 1,860 7 Calcium (Ca) < 515 < 3,660 21,000 17,200 33,000 7,860 < 13,900 2 Chlorine (Cl) < < Iron (Fe) 2,070 4, ,740 2,650 9,080 3,580 4 Magnesium (Mg) 3,440 3,390 2,820 4,520 2,080 1,120 2,900 5 Manganese (Mn) 274 2, ,640 3,010 2,270 6 Sodium (Na) , ,050 2,010 1,330 8 Titanium (Ti) 6,300 1,970 15,500 3,230 < 1,060 < 984 < 4,

10 C1 C2 I S - 9 -

11 WG WV Fig. 1. Scanning electron micrographs of residuals (100 X) Deflocculation (or Repulping ) of Residuals Due to dewatering, as-received residuals contained fibrous clumps that consist of wood fibers, clay (if any), and other particulates (if any). These clumps may be considered as weaker spots in concrete compared with well-dispersed individual fibers and particles. Also, in order for the fibers to function as fibers, they must be separated into individual fibers. Therefore, all seven sources of residuals were deflocculated, or repulped, into separated wood fibers and particulates (if any) before their addition to the concrete mixture. The pulper used for this purpose in the laboratory consisted of a 19-liter (5-gal.) plastic bucket and a high-speed mixer with a spinning rotor positioned above the bottom of the bucket. Mechanical repulping was performed by immersing the residuals in room-temperature water in the bucket and subjecting the mixture to a high-speed rotation by the rotor blades for not less than 20 minutes. Residuals C1, C2, WG, and BR deflocculated readily upon mechanical repulping. However, it took higher mixing speed and longer mixing time to deflocculate Residuals I, S, and WV. The reason for this was attributed to higher-degree dewatering of I, S, and WV residuals

12 SPECIMEN PREPARATION Mixing was done according to ASTM C 192 using a revolving drum, tilting mixer. Before starting rotation of the mixer, coarse aggregate and some of the mixing water (or a mixture of water and repulped residuals) were added. Then the mixer was started and was stopped after it turned a few revolutions. Then, sand was added, and the mixer was started and stopped again after it turned a few more revolutions. Then cement, the rest of the mixing water (or mixture of water and residuals), and chemical admixture (if used) were added. After all ingredients were in the mixer, the concrete was mixed for three minutes followed by a 3-minute rest, followed by additional two minutes of final mixing. When necessary, either water or HRWRA was incrementally added during the mixing process to modify the concrete mixture to the desired slump. Properties of freshly mixed concrete were determined (Table 8), and test specimens were cast for the evaluation of mechanical properties and durability of concrete. Specimens were demolded 24 ± 8 hours after casting and cured in lime-saturated water at 23 ± 2 C. MAJOR FINDINGS FROM PRELIMINARY INVESTIGATION Series of preliminary concrete mixtures were made to establish mixture proportions for concrete containing paper mill residuals. Major findings from the preliminary investigation were as follows: 1. Residuals do not affect compressive strength development of concrete. 2. With proper combination of residuals and HRWRA, slump and compressive strength of concrete can be adjusted. 3. Practically, by achieving equivalent density, equivalent-strength residuals concrete can be produced

13 MAIN MIXTURES MIXTURE PROPORTIONS, RESULTS, AND DISCUSSIONS Mixture Proportions Based on the mixture proportions established during the preliminary investigation, concrete mixtures were produced in the laboratory in two groups: (1) Reference 1 (plain), C1, WG, C2, and WV; and (2) Reference 2 (plain), BR, I, and S. As-received residuals content by mass of concrete was 0.65 % for C1, C2, WG, WV, I, and S; and 0.35 % for BR. Mixture proportions and fresh concrete properties are presented in Table 8. Table 8. Mixture Proportions and Fresh Properties of Concrete (Main Mixtures) Mixture Name Ref. 1 C1 C2 WG WV Ref. 2 BR I S Residuals, as-recd (% of conc. by mass) Wood Fibers (kg/m 3 )* Residuals, as-recd (kg/m 3 ) HRWRA (L/m 3 ) Cement (kg/m 3 ) Sand, SSD (kg/m 3 ) Coarse Agg., 19-mm max., SSD (kg/m ) Water (kg/m 3 ) W/Cm Slump (mm) Air Content (%) Density (kg/m 3 ) * From residuals. On dry basis. Depending on the source of residuals, amount of wood fibers (dry basis) in concrete varied between 2.4 to 4.9 kg/m 3 (4.0 to 8.3 lb/yd 3 ). In general, to keep the slump within the range of 75 to 150 mm (3 to 6 in.), higher dosage of high-range water-reducing admixture (HRWRA) was required for concrete with higher wood fiber content. Air-entraining admixture

14 (AEA) was not used. Density values of fresh concrete mixtures were almost uniform. In general, air contents of reference and residuals concrete mixtures were similar (1.8 vs. 1.9 % on average). Test Methods Overview of tests methods, specimens, and test ages is presented in Table 9. Time of Setting Time of setting test results are presented in Table 10 and Fig. 2. Time of setting of mortar fraction of concrete increased in proportion to HRWRA content of concrete. Since HRWRA was used approximately in proportion to wood fiber content, concrete containing residuals showed longer times of setting than the Reference Concrete. Table 9. Test Methods, Specimens, and Test Ages (Main Mixtures) ASTM Test Specimens Test Age, day(s) Number of Specimens per Test Age C 403 Time of Mortar obtained by sieving fresh concrete 0 2 Setting through a 4.75-mm sieve C 39 Compressive 100 x 200 mm cylinders 7, 28, 3 Strength 91 C 1399 Avg. Residual- Strength 100 x 100 x 350 mm beams # C 157 Length Change 75 x 75 x 285 mm prisms 1 3 C 944 Abrasion Top surface of 45-mm thick slices saw-cut 28 3 C 1202 C 666, A C 672 Resistance* Resistance to Chloride-Ion Penetration Resistance to Rapid Freezing and Thawing Salt-Scaling Resistance from the top of 150 x 300 mm cylinders 50-mm thick slices saw-cut from the top of 100 x 200 mm cylinders x 100 x 400 mm beams 42 3 Top surface of 225 x 225 x 75 mm blocks 28 2 * Double load (197 N) was used. Test start age Moist-cured until the age of 14 days, and then cured in air for 14 days at 23 ± 2 C and 50 ± 5 % relative humidity. # One specimen and two specimens were used for determining flexural strength and average

15 Time of Setting (hr) residual-strength, respectively. Table 10. Time of Setting and HRWRA Content Mixture Name Ref. 1 C1 C2 WG WV Ref. 2 BR I S Initial Setting Time (hr) Final Setting Time (hr) HRWRA (L/m 3 ) R 2 = R 2 = HRWRA Content (L/m 3 ) Final Setting Initial Setting Fig. 2. Relation between time of setting and HRWRA content of concrete Compressive Strength Test results for compressive strength of concrete are presented in Table 11 and in Fig. 3 and 4. Overall, average 28-day compressive strength was 43.2 MPa (6270 psi). In these particular groups of mixtures, residuals concrete showed average of about 15% lower 28-day compressive strength than the Reference Concrete. Reference and residuals concrete mixtures showed similar patterns of strength development

16 Compressive Strength (MPa) Compressive Strength (MPa) Table 11. Compressive Strength of Concrete (in MPa) Age (days) Ref. 1 C1 C2 WG WV Ref. 2 BR I S Ref. 1 C1 C2 WG WV Age (days) Fig. 3. Compressive strength of concrete (C1, C2, WG, WV) Ref. 2 BR I S Age (days) Fig. 4. Compressive strength of concrete (BR, I, S)

17 Average Residual-Strength Overall, mean value of average residual-strength of concrete after cracking in flexure was about 1% of flexural strength (Table 12). In general, residuals concrete showed higher Residual Strength Index than the Reference Concrete (1.1 vs. 0.7 % on average). Table 12. Average Residual-Strength of Concrete Mixture Name Ref. 1 C1 C2 WG WV Ref. 2 BR I S Flexural Strength (MPa) Average Residual-Strength (MPa) Residual Strength Index* (%) Note: Properties in this Table of Ref. 1, C1, C2, WG, and WV were determined by testing recast beams and may not correlated with other properties such as compressive strength. * Residual Strength Index (%) = Average Residual-Strength / Flexural Strength x 100 Length Change Test results for length change (i.e., drying shrinkage) of concrete are shown in Table 13 and in Fig. 5 and 6. C1, C2, WG, and WV mixtures showed somewhat higher drying shrinkage than their reference mixture (Ref. 1). BR, I, and S mixtures showed a little lower drying shrinkage than their reference mixture (Ref. 2). Overall, drying shrinkage of residuals concrete was similar to that of the Reference Concrete. Table 13. Length Change of Concrete Due to Curing in Water and Drying in Air (in %) Mixture Age (days) Name Ref C C WG WV

18 Length Change (%) Length Change (%) Ref BR I S Age (days) Ref. 1 C1 C2 WG WV Fig. 5. Length change of concrete due to curing in water and drying in air (C1, C2, WG, WV) Age (days) Ref. 2 BR I S Fig. 6. Length change of concrete due to curing in water and drying in air (BR, I, S)

19 Resistance to Chloride-Ion Penetration Chloride-ion penetrability results are presented in Table 14. Lower charge passed implies higher resistance of concrete to chloride-ion penetration. Chloride-ion penetration resistance of residuals concrete was somewhat lower than the Reference Concrete. Table 14. Chloride-Ion Penetrability Into Concrete Mixture Name Ref. 1 C1 C2 WG WV Ref. 2 BR I S Charge Passed (coulombs) Chloride-Ion Penetrability Mod. Mod. High High High Mod. Mod. Mod. High Charge Passed (coulombs) Chloride-Ion Penetrability > 4,000 High 2,000-4,000 Moderate 1,000-2,000 Low 100-1,000 Very Low < 100 Negligible Abrasion Resistance Test results for mass loss of concrete due to abrasion are presented in Table 15 and in Fig. 7 and 8. Lower mass loss implies higher abrasion resistance of concrete. In general, abrasion resistance of residuals concrete was somewhat lower than the Reference Concrete. WV concrete showed about three times as much abrasion mass loss as Reference 1 concrete. Table 15. Cumulative Abrasion Mass Loss of Concrete (in grams) Abrasion Time (min.) Ref. 1 C1 C2 WG WV Ref. 2 BR I S

20 Mass Loss (g) Mass Loss (g) Abrasion Time (min) Ref. 1 C1 C2 WG WV Fig. 7. Mass loss of concrete specimens due to abrasion (C1, C2, WG, WV) Ref. 2 BR I S Abrasion Time (min) Fig. 8. Mass loss of concrete specimens due to abrasion (BR, I, S) Resistance to Rapid Freezing and Thawing Test results for freezing-and-thawing durability factor of concrete are presented in Fig. 9. Highest possible durability factor is 100, which means that dynamic modulus of elasticity of concrete did not decrease (no deterioration) after 300 cycles of freezing and thawing. A concrete beam is considered to have failed when its relative dynamic modulus of elasticity (RDMOE)

21 Mixture Name reaches 60 % of the initial modulus. If RDMOE is higher than 60 % at 300 cycles, durability factor is same as the RDMOE at 300 cycles. If a beam fails (RDMOE reaches 60 %) at N cycles before completing 300 cycles, its durability factor is calculated as 60 x N / 300. Test results for relative dynamic modulus of elasticity of concrete are shown in Table 16 and in Fig. 10 and 11. Concrete containing residuals generally showed much higher resistance to freezing and thawing than the Reference Concrete. Four out of seven residuals concrete mixtures showed durability factor of 85 or higher. Overall, durability factor of residuals concrete was twice as high (64 vs. 32 on average) as the Reference Concrete. This could be attributed to the reduced rate of crack propagation due to micro-fiber reinforcement of concrete [13, 14] with cellulose fibers. Ref C1 94 C2 44 WG 14 WV 23 Ref BR 94 I 85 S Durability Factor Fig. 9. Freezing-and-thawing durability factor of concrete

22 Relative Dynamic Modulus of Elasticity (%) Table 16. Change in Relative Dynamic Modulus of Elasticity (%) of Concrete Due to Cycles of Freezing and Thawing Mixture Freezing and Thawing Cycles Name Ref C C WG WV Ref BR I S Freezing and Thawing Cycles Ref. 1 C1 C2 WG WV Fig. 10. Change in relative dynamic modulus of elasticity of concrete due to cycles of freezing and thawing (C1, C2, WG, WV)

23 Relative Dynamic Modulus of Elasticity (%) Freezing and Thawing Cycles Ref. 2 BR I S Fig. 11. Change in relative dynamic modulus of elasticity of concrete due to cycles of freezing and thawing (BR, I, S) Salt-Scaling Resistance Test results of salt-scaling resistance of concrete are presented in Tables 17 and 18, and in Fig. 12 and 13. Concrete containing residuals generally showed much higher salt-scaling resistance than the Reference Concrete. Overall, residuals concrete withstood 2.8 times as many saltscaling cycles as the Reference Concrete (85 vs. 30 cycles on average) before reaching severe surface scaling. This was again attributed to reinforcement of concrete with wood fibers. Table 17. Salt-Scaling Resistance of Concrete Mixture Name Ref. 1 C1 C2 WG WV Ref. 2 BR I S Cycles to Reach Severe Scaling

24 Table 18. Salt Scaling of Concrete Salt-Scaling Scaling Rating* Cycle Ref. 1 C1 C2 WG WV Ref. 2 BR I S * Rating Scaling 0 none 1 very slight (3 mm depth, max, no coarse agg. visible) 2 slight to moderate 3 moderate (some coarse agg. visible) 4 moderate to severe 5 severe (coarse agg. visible over the entire surface)

25 Scaling Rating Scaling Rating Ref. 1 C1 C2 WG WV Salt Scaling Cycles Fig. 12. Salt scaling of concrete (C1, C2, WG, WV) Ref. 2 BR I S Salt Scaling Cycles Fig. 13. Salt scaling of concrete (BR, I, S)

26 ADDITIONAL MIXTURES MIXTURE PROPORTIONS, RESULTS, AND DISCUSSIONS Splitting Tensile and Flexural Strengths Splitting tensile and flexural strengths of plain concrete and residuals concrete were compared. Reference (plain) concrete did not contain any high-range water-reducing admixture (HRWRA), whereas residuals concrete contained 490 ml of HRWRA per 100 kg (7.5 fl oz/100 lb) of cement. Average wood fiber content in residuals concrete was about 0.85 % by mass of cement. As-received residuals content ranged from 0.44 to 0.78 % by mass of concrete. Air-entraining admixture (AEA) was not used. Mixture proportions and fresh concrete properties are presented in Table 19. Uniform density values of concrete were achieved. Air content values of the Reference Concrete and residuals concrete were similar (1.6 vs. 2.1 % on average). Table 19. Mixture Proportions and Fresh Concrete Properties (for Tensile and Flexural Strengths) Mixture Name Ref. WG I C1 S C2 WV BR Avg.* Residuals, as-recd (% of conc. by mass) Wood Fibers (dry basis) from Residuals (kg/m 3 ) Residuals, as-recd (kg/m 3 ) HRWRA (L/m 3 ) Cement (kg/m 3 ) Sand, SSD (kg/m 3 ) Coarse Agg., 19-mm max., SSD (kg/m ) Water (kg/m 3 ) W/Cm Slump (mm) Air Content (%) Density (kg/m 3 ) * For residuals concrete

27 Compressive, splitting tensile, and flexural strengths of concrete were determined at 28 days and the results are presented in Table 20 and Fig. 14. Using the equations shown in Fig. 14, it is expected that residuals concrete of same compressive strength as the Reference Concrete would have splitting tensile and flexural strengths of about 4.80 and 5.75 MPa (696 and 834 psi), respectively. These values are about 4 and 17 % higher than the corresponding actual values of the Reference (plain) concrete. Conversely, at the same level of splitting tensile or flexural strength, residuals concrete showed lower compressive strength than the Reference Concrete. Table 20. Compressive, Splitting Tensile, and Flexural Strength of Concrete at 28-days (in MPa) Strength Ref. WG I C1 S C2 WV BR Avg.* Compressive Splitting Tensile Flexural * For residuals concrete

28 Splitting Tensile or Flexural Strength at 28 Days (MPa) y = x R 2 = Flexural (Residuals Conc.) Flexural (Ref.) y = x R 2 = Compressive Strength at 28 Days (MPa) Splitting Tensile (Residuals Conc.) Splitting Tensile (Ref.) Fig. 14. Flexural and splitting tensile strengths of concrete in relation to compressive strength Response to AEA Responses of plain concrete and residuals concrete to air-entraining admixture (AEA) were compared. Reference (plain) concrete did not contain any high-range water-reducing admixture (HRWRA), whereas residuals concrete contained 490 ml of HRWRA per 100 kg (7.5 fl oz/100 lb) of cement. Average wood fiber content in residuals concrete was about 0.85 % by mass of cement. As-received residuals content ranged from 0.44 to 0.78 % by mass of concrete. For both the Reference Concrete and the residuals concrete, 175 ml of air-entraining admixture (AEA) was used per 100 kg (2.7 fl oz/100 lb) of cement. Mixture proportions and fresh concrete properties are presented in Table 21. Compressive strength results are presented in Table 22 and Fig. 15. Table 21. Mixture Proportions and Fresh Concrete Properties (for Response to AEA) Mixture Name Ref. WG I C1 S C2 WV BR Avg.* Residuals, as-recd (% of conc. by mass)

29 Wood Fibers (dry basis) from Residuals (kg/m 3 ) Residuals, as-recd (kg/m 3 ) HRWRA (L/m 3 ) AEA (L/m 3 ) Cement (kg/m 3 ) Sand, SSD (kg/m 3 ) Coarse Agg., 19-mm max., SSD (kg/m 3 ) Water (kg/m 3 ) W/Cm Slump (mm) Air Content (%) Density (kg/m 3 ) * For residuals concrete Table 22. Compressive Strength of Concrete (Response to AEA) (in MPa) Age (days) Mixture Name Ref. WG I C1 S C2 WV BR Avg.* * For residuals concrete

30 Compressive Strength (MPa) Ref. WG I C1 S C2 WV BR Age (days) Fig. 15. Compressive strength of concrete (Response to AEA) Air content, unit weight, and 28-day compressive strength of the air-entrained Reference Concrete were 6.6 %, 2300 kg/m 3 (143 lb/ft 3 ), and 35.5 MPa (5150 psi), respectively. Corresponding average values for residuals concrete were 4.2 %, 2360 kg/m 3 (147 lb/ft 3 ), and 40.3 MPa (5840 psi). The results suggest that concrete containing residuals may require higher dosage of AEA compared with Reference (plain) concrete. As shown earlier in this paper, however, residuals concrete showed generally much higher resistance to freezing and thawing and to salt scaling than plain concrete without entrained air. CONCLUSIONS Based on the data presented, the following conclusions can be drawn:

31 1. Without the use of HRWRA, fibrous residuals from pulp and paper mills either reduce slump or increase water demand of concrete. 2. With proper dosage of HRWRA, slump and compressive strength of concrete containing the residuals can be managed as desired. In general, dosage of HRWRA was proportional to amount of wood fibers in concrete. Time of setting increased as the dosage of HRWRA increased. Residuals themselves do not affect strength development of concrete. 3. In general, at somewhat lower compressive strength, concrete containing the residuals showed higher average residual-strength, equivalent length change (drying shrinkage), and equivalent or lower chloride-ion penetration resistance and abrasion resistance when compared with reference concrete made without residuals. 4. On the other hand, the residuals concrete showed, in general, much higher freezing-andthawing resistance (durability factor: 64 vs. 32 on average) and salt-scaling resistance (number of cycles to reach severe scaling: 85 vs. 30 on average) than the reference concrete. This improvement was attributed to microfiber reinforcement of concrete with cellulose fibers. Both the residuals and the reference concrete mixtures were not air-entrained, but contained high-range water-reducing admixture (HRWRA). 5. At same level of compressive strength, residuals concrete showed about 4 and 17 %, respectively, higher splitting tensile and flexural strengths than reference concrete made without residuals. Again, the concrete mixtures were not air-entrained, but contained HRWRA. 6. When same dosage of air-entraining admixture (AEA) was used, residuals concrete showed lower air content (4.2 vs. 6.6 %) and higher compressive strength (40.3 vs MPa at 28 days) than plain concrete

32 ACKNOWLEDGEMENT The writers express deep sense of gratitude to U.S. Department of Energy Agenda 2020 Program; National Council of the Paper Industry for Air and Stream Improvement, Research Triangle Park, NC; Weyerhaeuser Company, Federal Way, WA; and Stora Enso North America Company, Wisconsin Rapids, WI for providing major funding for this project. The UWM Center for By-Products Utilization was established in 1988 with a generous grant from the Dairyland Power Cooperative, La Crosse, WI; Madison Gas and Electric Company, Madison, WI; National Minerals Corporation, St. Paul, MN; Northern States Power Company, Eau Claire, WI; We Energies, Milwaukee, WI; Wisconsin Power and Light Company, Madison, WI; and, Wisconsin Public Service Corporation, Green Bay, WI. Their financial support and additional grant and support from Manitowoc Public Utilities, Manitowoc, WI, are gratefully acknowledged. REFERENCES 1. Smook, Gary A., Handbook for Pulp and Paper Technologists, 2 nd Ed., Angus Wilde Publications, Bellingham, WA, June 1992, 419 pages. 2. Unwin, J., Why Bury It When You Can Use It?: NCASI s Support of the Industry s Efforts To Find Beneficial Uses For Solid Wastes, Proceedings of the 2000 NCASI National Meeting, Denver, CO, May 8-9, 2000, NCASI (National Council of the Paper Industry for Air and Stream Improvement, Inc.), Research Triangle Park, NC, 2000, pp Solid Waste Management and Disposal Practices in the U.S. Paper Industry, Technical Bulletin No. 641, NCASI, New York, NY, Scott, G., and Smith, A., Sludge Characteristics and Disposal Alternatives for Recycled Fiber Plants, 1995 Recycling Symposium, Technical Association of the Pulp and Paper Industry (TAPPI), Atlanta, GA, 1995, pp Alternative Management of Pulp and Paper Industry Solid Wastes, Technical Bulletin No. 655, NCASI, New York, NY,

33 6. Solid Waste Management Practices in the U.S. Paper Industry , Technical Bulletin No. 793, NCASI, Research Triangle Park, NC, Soroushian, P. and Marikunte, S., Reinforcement of Cement-Based Materials with Cellulose Fibers, Thin-Section Fiber Reinforced Concrete and Ferrocement, ACI Special Publication SP-124, Detroit, MI, 1990, pp Vinson, K. D. and Daniel, J. I, Specialty Cellulose Fibers for Cement Reinforcement, Thin Section Fiber Reinforced Concrete and Ferrocement, ACI Special Publication SP-124, Detroit, MI, 1990, pp Soroushian, P. and Marikunte, S., Moisture Sensitivity of Cellulose Fiber Reinforced Cement, Durability of Concrete, ACI Special Publication SP-126, Vol. 2, Detroit, MI, 1991, pp Soroushian, P., Marikunte, S., and Won, J., Statistical Evaluation of Mechanical and Physical Properties of Cellulose Fiber Reinforced Cement Composites, ACI Materials Journal, Vol. 92, No. 2, Detroit, MI, March-April 1995, pp Soroushian, P., Marikunte, S., and Won, J., Wood Fiber Reinforced Cement Composites under Wetting-Drying and Freezing-Thawing Cycles, Journal of Materials in Civil Engineering, ASCE, Vol. 6, No. 4, New York, NY, November 1994, pp Sarigaphuti, M., Shah, S. P., and Vinson, K. D., Shrinkage Cracking and Durability Characteristics of Cellulose Fiber Reinforced Concrete, ACI Materials Journal, Vol. 90, No. 4, Detroit, MI, July-August 1993, pp Pigeon, M., Pleau, R., Azzabi, M., and Banthia, N., Durability of Microfiber-Reinforced Mortars, Cement and Concrete Research, Vol. 26, No. 4, Pergamon Press, Tarrytown, NY, Apr. 1996, pp Pigeon, M., Azzabi, M., and Pleau, R., Can Microfibers Prevent Frost Damage? Cement and Concrete Research, Vol. 26, No. 8, Pergamon Press, Tarrytown, NY, Aug. 1996, pp Pierre, P., Pleau, R., and Pigeon, M., Mechanical Properties of Steel Microfiber Reinforced Cement Pastes and Mortars, Journal of Materials in Civil Engineering, Vol. 11, No. 4, American Society of Civil Engineers (ASCE), Reston, VA, Nov. 1999, pp Fiber Reinforced Concrete, Portland Cement Association, Skokie, IL, A Summary of Available Data on the Chemical Composition of Forest Products Industry Solid Wastes, Special Report No , NCASI, Research Triangle Park, NC, October

34 18. Naik, T. R., Paper Industry By-Products Utilization, Report No. CBU , UWM Center for By-Products Utilization, Department of Civil Engineering and Mechanics, University of Wisconsin-Milwaukee, February Naik, T. R., Use of Residuals in Production of Cellucrete, a report prepared for the Weyerhaeuser Company, Tacoma, WA, October Naik, T. R. and Kraus, R. N., Development of Concrete Utilizing Paper Mill Residual Solids, Report No. CBU , UWM Center for By-Products Utilization, Department of Civil Engineering and Mechanics, The University of Wisconsin-Milwaukee, November Chun, Y., Investigation on the Use of Pulp and Paper Mill Residual Solids in Producing Durable Concrete, PhD Thesis, Department of Civil Engineering and Mechanics, The University of Wisconsin-Milwaukee, December